In a semiconductor manufacturing process, circuit patterns formed on a semiconductor substrate (wafer) are rapidly becoming finer, and importance of process monitoring that monitors whether or not the patterns are formed as designed, for example, is increasing. For example, measurement and inspection of the circuit patterns or the like on the wafer are performed at the end of each manufacturing step in order to detect occurrence of an abnormality or a failure (a defect) in the semiconductor manufacturing process early or in advance.
During the above measurement and inspection, in a metrology/inspection apparatus, e.g., an SEM using a scanning electron beam technique, and a corresponding metrology/inspection method, a primary electron beam (an electron beam) is radiated to a sample such as the wafer to be measured/inspected while the sample is scanned with the primary electron beam, and an energy such as secondary electrons/reflection generated by this radiation is detected. An image (a measurement image or an inspection image) is then generated based on that detection by signal processing and image processing, and the measurement, observation, or the inspection is performed based on that image.
In the aforementioned metrology apparatus using the scanning electron beam technique, it is necessary to deflect the secondary electrons/reflected electrons (a secondary beam) generated from the sample towards a detector in order to detect the secondary electrons/reflected electrons with a high efficiency. Meanwhile, when a unit deflecting the secondary beam towards a predetermined direction affects the primary beam, a shift of a radiation position of the primary beam on the sample occurs, lowering a measurement accuracy of the apparatus. Therefore, a unit separating the primary beam and the secondary beam from each other is required, which deflects the secondary electrons/reflected electrons, i.e., the secondary electron beam, towards a direction to which the detector is arranged but does not deflect the primary beam radiated to a predetermined position of the sample.
A technique described in Japanese Unexamined Patent Application Publication No. 2006-332038 (Patent Literature 1) is an example of a conventional technique related to the above measurement and inspection and control of separation of the primary electron beam and the secondary electron beam.
Patent Literature 1 describes that, in an electromagnetic overlapping objective lens that can have an improved resolution, secondary electrons generated from a sample are accelerated, so that dependence of a rotation operation by the objective lens on secondary electron energy is suppressed. Also, it is described that, when a low elevation angle component and a high elevation angle component, seen from a portion of generation of the secondary electrons, and an azimuth component are chosen and detected by an annular detector provided between an electron source and the objective lens, a central axis of the secondary electrons concentrated by acceleration to be thinner is made coincident with a central axis of a low-elevation-angle signal detection system, and the secondary electrons are adjusted and deflected by E×B to avoid a hole in a high-elevation-angle signal detection system.